Electrical make-and-break contact



Patented Apr. 14, 1936 ELECTRICAL MAKE-AND-BREAK CONTACT Joseph A. Weiger, Indianapolis, Ind., assignor to P. R. Mallory & 00., Incorporated, Indianapolis, Ind., a corporation of Indiana No Drawing. Application January 30, 1933, Serial No. 654,362

7 Claims.

The invention relates to electrical make-andbreak contacts and, more particularly, to make and break contacts for closing and opening electrical circuits.

General objects of the invention are the provisions of electrical make-and-break contacts having improvedv operating characteristics and the composition from which such contacts are formed.

A more specific object of the invention is the provision of electrical make-and-break contacts formed from an alloy, which operate in an improved manner, are less susceptible to oxidation and have decreased arcing tendency as compared with the usual contacts in the same fields of use.

Another object of the invention is the provision of contacts of this type in which the usual deterioration, pitting and transfer of contact material from one contact to the other cooperating contact under ordinary arcing conditions are materially reduced; and which can be more cheaply produced than the contacts in common practice at the present time.

Among other objects which will in part be ob= vious and will in part appear hereinafter, the invention contemplates the composition of alloys from which make-and-break contacts having improved operating characteristics are fabricated.

The invention accordingly comprises a product possessing the features, properties, and the rela- 'tion of components which will be exemplified in the product hereinafter described and the scope of the application of which will be indicated in the claims.

Heretofore electrical make-and-break contacts have been extensively used in various applications, of which the use in automobile electrical systems may be taken as representative. Up to the present time such contacts have been made from various metals and alloys thereof, such as, for example, silver and other silver alloys. Upon breaking an electrical circuit arcing occurs. The usual contacts are subject to material deterioration under arcing, particularly where the electrical circuit is frequently broken and made. The faces of the contacts pit, fuse and volatilize under arcing, the latter being commonly accompanied by a transfer of contact material from one contact face to the other, resulting in the building up of a cone or cones on one contact face. This condition reduces the effective contact face area and often results in a complete failure of operation due to a short-circuiting through the building up of a cone suflicient in dimensions to close the circuit at all times.

In the relays used between the battery and the generator in automobile electrical systems many metals and alloys thereof have been experimentally used as contacts. But due to their many faulty operating characteristics, the use of silver contacts has become the general practice because of superior operating characteristics. Though comparatively efflcient in operation for such a use, silver is costly and for this reason contacts capable of as efflcient operation as are silver contacts, but which can be more cheaply produced than the latter, are highly desirable.

Contacts formed in accordance with the present invention not only avoid the ineflicient operating characteristics of prior contacts but attain an efliciency in operation even greater than that obtained with contacts formed from silver alone, and in addition can be more cheaply produced than can the silver contacts.

In carrying out the invention contact material is formed by alloying together silver, copper and nickel. Although the proportions of these elements may be varied to a certain extent without a loss of efllcient operating characteristics, their preferred proportions, given by way of example, 5:5 are approximately as follows:

7'7 per cent by weight of silver 20 per cent by weight copper 3 per cent by weight of nickel The improved contact material is a true alloy of the elements set forth above and may be ob tained in any well known and approved method of alloying metals.

The resulting alloy is cast into suitable form 3. and then swaged or rolled and drawn to a convenient shape, and made into suitable contacts by the usual heading machine method.

The proportions may be varied depending upon the requirements for particular applications. 40 The copper, nickel and silver are all essential elements to the alloy and are accordingly all present in more than negligible amounts. The nickel content is preferaby kept below about 5 per cent and the copper will normally be present in pro- 45 portions within the range of 5 to 30 per cent, the remainder being substantially all silver.

If the above proportions are varied, it is pref- "erable to keep the percentage of silver above the combined percentages of the other two elements 50 since an exceedingly low amount of silver apparently reduces the desirable operating characteristics obtained when the proportions of the elements are approximately those given by way of example. The two base metals, copper and nickel, have been found to increase the hardness and to decrease the oxidation and the are deterioration of the silver without destroying the ductility and workability of the silver when alloyed with the latter in proportionately large amounts. This is best shown by a series of comparative tests run with contacts formed from the present alloy and those formed from coin silver, the results or" which are given below.

Contacts fabricated in accordance with the present invention are found to efficiently attain the objects set forth above as evidenced by the following comparative tests made with contacts made in accordance with the present invention and coin silver contacts:

1. Life tests showed that the present contacts e not only equal to coin silver contacts but tly better than the latter.

She alloy from which the present contacts e made can be swaged, rolled, drawn and shaped as readily as can coin silver.

3. The present contacts as compared with coin silver contacts show; (:1) increased hardness, thus they are less susceptible to hammering efiects; (73) less susceptibility to breakdown due to arcing; and (c) less tendency to arc. The above characteristics obtain for these contacts longer life in service.

he density of the present alloy is approidmately 9.6 grams per c. c. as compared to about 10.3 grams per c. c. for coin silver, thus contacts made from the present alloy require about '3 per cent less metal by weight than dc contacts made from coin silver.

5. The tensile strength of the present alloy is about 43,400 pounds per square inch with an elon gation of 3d per cent in 2 inches while the tensile strength of coin silver under similar conditions was found to be 423180 pounds per square inch with an elongation of Bil per cent in 2 inches.

The economy of material obtained by virtue of the fact the density of the present alloy is less than that of coin silver is accompanied by a cost which is at least 13 per cent less than that of coin silver. Thus contacts are obtained in ac cordance with the present invention which exhibit better operating characteristics than com silver and other types of contacts in the same field oi use and which cost less to manufacture.

Since certain changes may be made in the above article and different embodiments of the invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense.

The specific application of the present contacts to relay operation in automobile electrical systems is given only by way of example and not in a limit ing sense since the present contacts can be used. wherever electrical make-and-break contacts are 5 required to attain operations possible with the use of or characteristic of contacts made in accordance with the present invention. 1

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

Having described my invention, what I claim as new and desire to secure by Letters Patent, is:

l. An electrical make-and-breals contact composed of an alloy of silver, copper and nickel in which the copper and nickel combined bear a ratio in weight of about 1:3 to the silver and the nickel comprising not more than about 5 per cent by weight of the whole composition.

2. An electrical make-and-breair contact composed of an alloy the major portion oi which comprises silver combined with copper whis bears a ratio in weight of about lzd to the silt" and the remainder of niclrel comprising not more than about 5 percent by weight 0:? the whole composition.

3. an electrical malse-and-brealz contact corn-= posed of an alloy comprising from 65 per cent to 90 per cent by weight of silver with copper and nickel forming the essential elements of the i mainder, the copper comprising between 5 per cent and to per cent by weight 01 the whole cornposition and the nickel comprising not more than about 5 per cent of the whole composition.

4. electrical make-and-breal: contact com posed of an alloy comprising substantially 7'? per cent by weight of silver, 26 per cent by weight of copper and 3 per cent by weight of nickel.

5. An electrical substitute for silver composed of silver, nickel and copper in appromately the proportions: Silver 65%, copper 30%, nickel 5%.

6. [in electrical mahe-and-break contact com= 4 posed of more than negligible amounts and up to 5 per cent nickel, 5 to 39 per cent copper and the remainder silver.

7. An electrical make-and-breal: contact composed of more than negligible amounts up to 5 per cent nickel, 5 to 30 per cent copper, and the remainder substantially all silver, characterized by greater hardness, greater are resistance and less density than coin silver.

JOSEPH A. wsrom. 

